Today's electronically controlled fuel systems typically include numerous electrical actuators whose activation is controlled by an electronic controller. For instance, fuel injectors may include one or more electrical actuators to control injection timing and/or injection quantity. In common rail fuel systems, an electronically controlled pump or other actuator may control pressure in a common rail that supplies pressurized fuel to a bank of fuel injectors. While both piezo and solenoids are known for use as electrical actuators in fuel systems, solenoids continue to dominate in most applications. Over the years, there has been a continuous effort to improve actuator performance through various solenoid design strategies, pressure control strategies, mass property improvements, control wave forms and other considerations in an effort to improve consistency, robustness and speed, as well as other performance characteristics.
Co-owned U.S. Pat. No. 4,922,878 teaches a typical wave form control strategy for energizing a solenoid of a fuel injector to perform an injection event. The '878 patent teaches an electronic controller that has the ability to briefly apply a substantially higher voltage to the solenoid circuit to initiate movement of an armature of the solenoid to commence an injection event. For instance, this higher voltage may be supplied by capacitors that are continuously charged from system voltage “battery” between injection events. In order to hasten the time delay between initially applying a voltage to the solenoid circuit and the time at which the armature actually starts moving, the conventional wisdom has been to maintain the elevated voltage across solenoid circuit until the solenoid armature begins moving from its initial air gap position toward its final air gap position. During this initial period, current in the solenoid circuit is controlled to have a saw tooth pattern by the electronic controller maintaining current between a minimum and a maximum current by opening the circuit when the maximum circuit is reached, then closing the circuit at the minimum current, and repeating this process during what is commonly referred to as the pull-in duration. At the end of the pull-in duration, the controller may then drop to a battery voltage and a lower tier average current since less energy is needed to continue movement of the armature, and maybe even less energy needed to hold the armature at its final air gap position. These lower tiered current levels after the pull-in duration are often referred to as hold-in current levels.
As is well known in the art, movement of the solenoid armature changes a pressure configuration within the fuel injector causing a fuel injection event to occur. When it comes time to end the injection event, the circuit is opened, current decays and a bias (e.g. spring) moves the armature back toward its initial air gap position to again change a pressure condition within the fuel injector and end the injection event. While this type of wave form control strategy has worked well for many years, there are continued efforts being made to decrease hardware requirements and reduce power/energy requirements without compromising performance.
The present disclosure is directed toward one or more of the problems set forth above.